Advances in semiconductor manufacturing technologies have resulted in dramatically increased circuit packing densities and higher speeds of operation. In order to achieve such increased densities and circuit speeds, a wide variety of evolutionary changes have taken place with respect to semiconductor processing techniques and semiconductor device structures.
Some of the more recent changes in metal-oxide-semiconductor field effect transistor (MOSFET) semiconductor processing and device structures include gate replacement structures and manufacturing methods for such. In gate replacement, conventional polysilicon-based gate stack structures are removed after source/drain formation, and a gate stack with a high-k gate dielectric layer and a metal gate electrode (HKMG) are provided in their place. Various combinations of metals and metal alloys are selected by manufacturers to set a nominal value for the work function of the gate electrode. Such efforts are commonly referred to as work function engineering. It is well-known that the work function of the gate electrode is one of the factors in establishing the threshold voltage of a MOSFET.
In addition to changes in the gate stack structure, changes in the semiconductor body underlying the gate stack have also been adopted. A partial list of these changes includes the use of complex doping profiles, strained silicon, fully depleted silicon-on-insulator, raised source/drains, epitaxial silicon layers and finFET structures.
Typically, a semiconductor manufacturer develops a process, and then provides electrical modeling data and physical layout rules to chip designers. Chip designers, or more commonly the company by which the chip designers are employed, arrange for production of their circuit designs as integrated circuits fabricated by the semiconductor manufacturer.
As new transistor structures become available, where those new structures have certain desirable electrical properties, chip designers often wish to take advantage of those desirable electrical properties in at least some portion, or subset, of the circuitry in an existing chip design. By way of example, System on a Chip (SoC) devices often include blocks of pre-designed circuitry some of which may be supplied from different vendors. In order to get the desired performance from each of those blocks, different transistor characteristics may be needed in the different blocks. Put differently, it may be desirable to include a plurality of transistor types having various combinations of channel structures and gate stacks.
What is needed are integrated circuits with multiple transistor structures, each with its own unique electrical characteristics, and methods of integrating the manufacture thereof into a single process flow.